Marija Gligora

The relationship between phytoplankton species dominance and environmental variables in a shallow lake (Lake Vrana, Croatia)

The shallow Lake Vrana was studied over a 1-year period, special attention being paid to the phytoplankton. Phytoplankton was investigated monthly with respect to temporal variability of selected environmental factors. The regular annual development observed was in species contribution to total biomass rather than in seasonal changes in species composition. The assemblage was dominated by Cosmarium tenue Arch. and Synedra sp. In winter and in spring the phytoplankton assemblage was dominated by Cosmarium tenue and high contribution of Synedra sp. was observed during the summer and autumn. Results suggest that concentrations of inorganic nitrogen and phosphorus were critical in regulating phytoplankton biomass and species dominance.

Seasonal distribution and morphological changes of Ceratium hirundinella in two mediterranean shallow lakes

Seasonal distribution and morphological changes in two forms of Ceratium hirundinella in the shallow karstic Mediterranean lakes, Ponikve and Njivice, during 1997/98 and 2000/01, were studied. C. hirundinella f. gracile was present during the whole investigation period in Lake Njivice. The same species was the dominant form in Ponikve Lake during 1997/98, while in 2000/01 a strong development of C. hirundinella f. austriacum occurred. The species C. hirundinella f. austriacum was restricted to spring–summer time. This population showed larger variations in number of horns. An analysis of morphometric measurements showed significant differences (p<0.01) in the total length of cells, length of the fourth horn and V3 angle of the two Ceratium forms.

Observations on the diatom Navicula hedinii Hustedt (Bacillariophyceae) and its transfer to a new genus Envekadea Van de Vijver et al. gen. nov.

The population of an unknown naviculoid diatom from Lake Vrana in Croatia was identified as Navicula hedinii, a species described in 1922 from a small lake in eastern Turkestan (China). This species has some similarities with Navicula pseudocrassirostris, a marine species found in European coastal waters. Based on the ultrastructure of the two species, they can no longer be included within the taxonomical concept of Navicula sensu stricto. Following a comparative morphological analysis of both species with genera bearing similar characters (Adlafia, Veigaludwigia, Kobayasiella, Cavinula, Stenoneis, Climaconeis, Berkeleya, Sellaphora, Cosmioneis), a new genus, Envekadea is proposed for the two species. The new genus is characterized by a sigmoid raphe course with golfclub-like terminal fissures deflected in opposite directions, the areolae covered by external porous hymenes and the presence of one chloroplast, H-shaped in valve view.

Seasonal variation of organic compounds in a eutrophic oxbow lake

In may lakes, high planktonic biomass generates such large quantities that bottom waters become anoxic (Baranovic et al. 1993, Bardosi et al. 2000, Devai et al. 2002, Padisak et al. 2003), and massive organic-mineral aggregates occur in the water column, depending on meteorological and biomechanical conditions in the water coloumn (Stachowitsch et al. 1990; Degobbis et al. 1995). Chemical and physical speciation of dissolved organic carbon (DOC) impact the formation of aggregates in marine environment, but few studies have addressed the speciation of DOC in lacustrine ecosystems (V-Balogh et al. 2003). This study reports seasonal variability of DOC, total dissolved carbohydrates (TDCHO), total dissolved free amino acids (TDFAA), and colloidal organic carbon (COC > 1 kDa) in a eutrophic oxbow lake.